Fateful QB decision: If carried out as expected, the San Francisco 49ers' move to replace Alex Smith with Colin Kaepernick will be the most scrutinized decision in the NFL this week and perhaps all season.

Smith has completed 25 of his past 27 passes. The 49ers have posted a 19-5-1 record the past two seasons with Smith in the lineup. Smith has 38 touchdowns with 11 interceptions in his past 30 starts dating to late in the 2010 season. His Total QBR score has risen from a sub-average 45.8 last season to 69.8 this season. The latter figure ranked ninth in the NFL through Week 11 and would represent Pro Bowl-caliber play if sustained over a full season.

What's not to like? Smith ranks only 25th in third-down QBR at 32.0. That is up from 22.0 last season, but it's still not good enough.

Smith has done a disproportionate amount of damage on early downs, when opponents must account for the 49ers' formidable ground game. His QBR score on first and second downs has jumped from 55.9 last season to 80.8 this season. Might the lagging third-down production point to limitations the 49ers think Kaepernick can transcend?

Kaepernick hasn't played enough to draw meaning from his third-down performance. So far, though, so good. The second-year pro has completed 7 of 12 passes for 123 yards on third down. He has one passing touchdown and one rushing touchdown. His third-down QBR score (65.6) would mark a significant improvement if maintained over time.

Aldon Smith (99) is poised to become the NFL's all-time leader in sacks over a player's first two seasons. AP Photo/Paul Connors

Chasing down history: 49ers outside linebacker Aldon Smith needs two sacks to pass Derrick Thomas and tie Reggie White for the most sacks in a player's first two seasons since 1982, when sacks became an official stat. White had 31 in 1985-86. Thomas had 30 in 1989-90. Smith has 15 this season after collecting 14 as a rookie. Denver's Von Miller ranks sixth on the list with 24.5 in his first two seasons heading into Week 12.

Fresh-faced QBs: Kaepernick, Seattle's Russell Wilson and Arizona's Ryan Lindley had not started an NFL game before this season. All three are expected to start in Week 12. That makes St. Louis' Sam Bradford, with 36 career starts, the most seasoned starting quarterback in the division this week. The NFC West is bucking a broader NFL trend, however. Teams will have used no more than 42 starting quarterbacks through Week 12, the fewest to this point in any of the past 20 seasons, according to Elias Sports Bureau.

Hitting the road: Wilson has gone 5-0 at home with 11 touchdowns, zero interceptions and a 67.7 QBR score in those games. He heads to Miami in Week 12 having posted a 1-4 record on the road with four touchdowns, eight picks and a 47.3 QBR score. It's looking up for Wilson on the road, however. He completed 71.4 percent of his passes for 236 yards, two touchdowns and a 93.7 QBR score in his most recent road game, at Detroit. He's got a 70.7 QBR score for his past three road games, up from 23.6 for his first two. My feel is that Wilson has improved overall in recent weeks and that should translate to the road as long as his overall trajectory remains upward.

Welcoming back Wells: Running back Beanie Wells' return from a toe injury comes after the Cardinals pumped up their yards-per-carry average from a league-worst 3.5 through Week 8 to an 11th-ranked 4.3 since Week 9, a span of two games for Arizona. Wells faces a St. Louis run defense that has improved since he gashed it for 228 yards in Week 12 last season. The Rams are allowing 4.1 yards per carry, down from 4.8 last season. No Rams team has allowed fewer yards per carry over a season since 2002. On a side note, the Cardinals need no worse than a tie to avoid becoming the first NFL team to lose seven consecutive games after a 4-0 start.